Skeletal System, Bone Structure, and Joints: Exam Review Study Notes

Skeletal System Overview

Functions and Components of the Skeletal System

The skeletal system provides structural support, protection for internal organs, facilitates movement, stores minerals, and produces blood cells.

• Support: Framework for the body, maintaining shape and posture.

• Protection: Shields vital organs (e.g., skull protects the brain, rib cage protects the heart and lungs).

• Movement: Bones act as levers for muscles to produce movement.

• Mineral Storage: Reservoir for calcium and phosphorus.

• Blood Cell Production: Hematopoiesis occurs in red bone marrow.

Bone Classification and Structure

Types of Bones and Examples

Bones are classified by shape and structure, each serving specific functions.

• Long Bones: Longer than wide (e.g., femur, humerus).

• Short Bones: Cube-shaped (e.g., carpals, tarsals).

• Flat Bones: Thin and broad (e.g., sternum, skull bones).

• Irregular Bones: Complex shapes (e.g., vertebrae, pelvis).

• Sesamoid Bones: Embedded in tendons (e.g., patella).

Gross Anatomy of Long Bones

• Diaphysis: Shaft of the bone, composed of compact bone.

• Epiphysis: Ends of the bone, mostly spongy bone.

• Metaphysis: Region between diaphysis and epiphysis; contains growth plate.

• Medullary Cavity: Central cavity containing yellow marrow (fat storage).

• Periosteum: Dense connective tissue covering the bone surface.

• Endosteum: Membrane lining the medullary cavity.

Bone Markings

Bones have various markings for muscle attachment, articulation, and passage of nerves/vessels.

• Foramen: Opening for nerves and blood vessels.

• Fossa: Shallow depression.

• Condyle: Rounded articular projection.

• Process: Any bony prominence.

• Additional info: Other markings include tuberosity, crest, spine, and head.

Microscopic Structure of Bone Tissue

Compact vs. Spongy Bone

• Compact Bone: Dense, forms the outer layer; contains osteons (Haversian systems).

• Spongy Bone: Porous, found in epiphyses; contains trabeculae and red marrow.

Bone Cells

• Osteoblasts: Bone-forming cells; synthesize bone matrix.

• Osteocytes: Mature bone cells; maintain bone tissue.

• Osteoclasts: Bone-resorbing cells; break down bone matrix.

• Osteoprogenitor Cells: Stem cells that differentiate into osteoblasts.

Bone Development and Growth

Intramembranous vs. Endochondral Ossification

• Intramembranous Ossification: Bone develops from fibrous membranes (e.g., flat bones of skull).

• Endochondral Ossification: Bone forms by replacing hyaline cartilage (e.g., long bones).

Growth and Remodeling

• Epiphyseal Plate: Site of longitudinal growth in children and adolescents.

• Bone Remodeling: Continuous process involving osteoblasts and osteoclasts.

• Hormonal Regulation: Growth hormone, sex hormones, and parathyroid hormone influence bone growth.

Axial and Appendicular Skeleton

Axial Skeleton

• Components: Skull, vertebral column, rib cage.

• Function: Protects central nervous system and thoracic organs.

Appendicular Skeleton

• Components: Limbs and girdles (pectoral and pelvic).

• Function: Facilitates movement and interaction with environment.

Joints (Articulations)

Classification of Joints

• Fibrous Joints: Immovable; bones joined by dense connective tissue (e.g., sutures in skull).

• Cartilaginous Joints: Slightly movable; bones joined by cartilage (e.g., intervertebral discs).

• Synovial Joints: Freely movable; characterized by joint cavity and synovial fluid (e.g., knee, shoulder).

Types of Synovial Joints

• Ball-and-Socket: Multiaxial movement (e.g., shoulder, hip).

• Hinge: Flexion and extension (e.g., elbow, knee).

• Pivot: Rotation (e.g., atlas and axis in neck).

• Saddle: Allows movement in two planes (e.g., thumb).

• Plane: Gliding movements (e.g., intercarpal joints).

• Condyloid: Movement in two planes (e.g., wrist).

Joint Movements

• Flexion/Extension: Decreasing/increasing angle between bones.

• Abduction/Adduction: Movement away/toward midline.

• Rotation: Movement around longitudinal axis.

• Circumduction: Circular movement combining flexion, extension, abduction, and adduction.

Bone and Joint Disorders

Common Disorders

• Osteoporosis: Decreased bone density, increased fracture risk.

• Arthritis: Inflammation of joints; includes osteoarthritis and rheumatoid arthritis.

• Fractures: Breaks in bone; classified by type (simple, compound, comminuted, etc.).

Selected Bone and Joint Structures

Major Bones and Landmarks

• Skull: Contains cranial and facial bones; protects brain and sensory organs.

• Vertebral Column: Cervical, thoracic, lumbar, sacral, and coccygeal regions.

• Rib Cage: Sternum and ribs; protects thoracic organs.

• Upper Limb: Humerus, radius, ulna, carpals, metacarpals, phalanges.

• Lower Limb: Femur, tibia, fibula, tarsals, metatarsals, phalanges.

• Girdles: Pectoral (clavicle, scapula) and pelvic (ilium, ischium, pubis).

Selected Joints and Their Functions

• Knee Joint: Hinge joint; allows flexion and extension.

• Shoulder Joint: Ball-and-socket; greatest range of motion.

• Hip Joint: Ball-and-socket; supports body weight.

• Elbow Joint: Hinge; allows flexion and extension.

Table: Classification of Bones

Bone Type	Shape	Example	Main Function
Long	Longer than wide	Femur, humerus	Movement, support
Short	Cube-shaped	Carpals, tarsals	Stability, support
Flat	Thin, broad	Sternum, skull	Protection
Irregular	Complex shapes	Vertebrae, pelvis	Protection, support
Sesamoid	Embedded in tendons	Patella	Reduce friction, modify pressure

Selected Equations and Formulas

• Bone Density: $\text{Bone Density} = \frac{\text{Bone Mass}}{\text{Bone Volume}}$

• Leverage (Mechanical Advantage): $\text{Mechanical Advantage} = \frac{\text{Length of Effort Arm}}{\text{Length of Resistance Arm}}$

Additional info:

• Hormones such as calcitonin and parathyroid hormone regulate calcium levels and bone remodeling.

• Ligaments connect bone to bone, while tendons connect muscle to bone.

• Synovial fluid lubricates joints and reduces friction.